Hot water cylinder

The hot water cylinder, often referred to as the hot water tank, is a vessel designed for heating and storing hot water for use in the home. It is typically made out of copper, and has a concave base for structural integrity. The top of the cylinder, or crown as it’s known, is usually bell-shaped in order to prevent air locks.

The hot water cylinder is usually situated in an airing cupboard. It is usually fed from the cold water storage cistern in the loft; however in some installations, the cold water cistern may be situated on a platform directly above it, or may even be part of the cylinder itself.

The water inside the cylinder is heated by water from the central heating circuit. Hot water from the boiler flows through the cylinder via a heat exchanger which consists of a coil of copper pipework. Such cylinders are also fitted with an electric immersion heater as a backup. This type of arrangement is known as an indirect hot water cylinder, due to the fact that the two bodies of water do not (and should not) come into contact with each other. Another kind of cylinder, known as a primatic hot water cylinder, separates the two bodies of water via an air bubble. Some cylinders are heated via electric immersion heaters only, and do not have an internal heat exchanger. These are known as direct hot water cylinders.

Cylinders fed via the cold water tank are classified as open or vented, due to the fact that the water is held at atmospheric pressure. However, unvented, mains-fed cylinders are becoming increasingly common, and do not require a cold water storage cistern.

Overview

The hot water cylinder is supplied with cold water via a 22 mm downpipe from the cold water tank. In larger households, a 28 mm pipe may be necessary.

It is gravity acting on the water in the cold water tank which effectively pushes hot water out of the top of the cylinder. Therefore the cold feed must be fitted with a gate valve so that the domestic hot water can be shut off if necessary. The cold feed must also be fitted with a drain-cock so that the cylinder can be emptied, as shutting off the cold feed will not empty the cylinder.

On an indirect cylinder, the flow from the boiler enters at the top of the coil, with the return exiting at the bottom. These are typically 22 mm fittings.

Water exits the top of the cylinder via a 22 mm draw-off. This pipe usually runs across the top of the cylinder towards the wall, at which point it is tee’d off, with the lower aspect supplying all of the domestic hot water services, and the other aspect rising up into the loft and bending over into the cold water tank, but without dipping into the water. This pipe is known as the expansion pipe. In order to prevent air from becoming trapped in the draw-off pipe at the top of the cylinder, it is important that it rises slightly as it runs towards the wall in the airing cupboard. This will prevent the formation of air locks.

When water in the cylinder is heated, air bubbles form.. The crown of the cylinder is usually in the shape of a curved bell so that air can rise up and out of the cylinder, instead of becoming trapped and forming airlocks in the system. Air bubbles should rise out of the cylinder and up through the expansion pipe. As the name implies, the expansion pipe also allows for the expansion of the water in the cylinder when it is heated, and for it to discharge harmlessly into the cold water tank if necessary. The expansion pipe and cold water tank act as a kind of safety valve for the cylinder, as it would be extremely dangerous to contain hot water without allowing for changes in its volume.

Immersion heater

On an indirect cylinder, the immersion heater enters the cylinder via the crown, pointing inwards towards the central body of water. A standard immersion heater consists of a 240 volt, 3 kilowatt element, and is secured to the cylinder via a 2 and a quarter inch BSP thread boss. The advantage of having an immersion heater on an indirect hot water cylinder is that even if the boiler fails, the household will still have hot water.

A direct hot water cylinder will have two immersion heaters, each entering the cylinder horizontally: one towards the bottom of the cylinder, and another around two thirds of the way up. A household with a direct cylinder will typically be on an Economy 7 electricity tariff, which offers cheaper rates for off-peak times.

Operated by a timer and located near the base of the cylinder, the bottom immersion heater will heat the entire cylinder using cheaper night time electricity. In contrast, the higher immersion heater heats mainly the top third of the cylinder, and will come on when water is drawn off during the day. It may also periodically switch on in order to keep the water in the cylinder at the desired temperature.

Thermostat

An immersion heater will have its own adjustable thermostat. This slides into the cylinder in its own pocket without coming into contact with the water. In order to minimise the risk of scalding and to prevent the growth of Legionella, the thermostat should be set to 60° C.

Construction & capacity

Hot water cylinders are typically made out of copper, and have a capacity of either 120 litres, 144 litres, or 210 litres. These are 90 cm, 105 cm, and 150 cm tall respectively. A 210 litre cylinder will be necessary for an Economy 7 tariff, ensuring that the water is heated cost-effectively.

The cylinder will be very heavy when full of water, and should be situated on a flat, stable, continuous wooden base – ideally ¾ inch plywood across three timber bearers. Air gaps between the timber bearers will permit the circulation of air under the cylinder, limiting the formation of condensation.

When replacing an immersion heater, it is good practice to leave water in the cylinder where it is possible to do so. The mass of water will support the cylinder wall when unscrewing the immersion heater, and help to prevent it from warping.

Due to their size and copper construction, old hot water cylinders may fetch anywhere up to £100 at a scrap dealer.

Insulation

Preventing heat loss is one of the most effective ways of saving energy in the home, and the hot water cylinder is no exception. A specially made, glass fibre insulation jacket which is strapped around an exposed copper cylinder only costs a few pounds, and will almost certainly pay for itself within a few months. Most hot water cylinders available on the market today are sprayed with a layer of foam insulation, which is even more effective.

Thermostat

Not to be confused with the immersion heater thermostat, indirect hot water cylinders are fitted with a thermostat which is typically strapped to the side of the cylinder around a third or a half of the way up from the bottom.

When the water in the cylinder reaches the pre-set temperature, the cylinder thermostat will close the motorised valve, preventing the flow of hot water from the boiler through the coil.

In order to detect the temperature of the water accurately, a cylinder thermostat must come into contact with the copper wall of the cylinder. This will require any pre-existing foam insulation to be cut away where the thermostat is to be fitted.

Flanges

Surrey flange

A Surrey flange creates an additional draw-off point from the top of the cylinder, which is typically used as a dedicated supply for a shower pump. It does this via a tube which dips down into the cylinder and draws water from the main body of water. This ensures that the pump is not damaged by air bubbles which form during the heating of the water – these are still allowed to rise to the highest point of the cylinder and out at the top through the main draw-off point before being expelled through the expansion pipe.

Essex flange

An Essex flange is another way of establishing a dedicated feed for a shower pump and protecting it from air damage. It draws water from the side of the cylinder, slightly below the crown.

One of the advantages of an Essex flange over a Surrey flange is that there is no need to modify the existing pipework above the cylinder. However, fitting an Essex flange will require a hole to be cut in the side of the cylinder. Some cylinders come with an Essex flange pre-fitted by the manufacturer.

Secondary return

Hot water cylinders can also accommodate a secondary return. This is a configuration in which hot water is pumped from the cylinder and around a circuit, before returning to the cylinder.

By drawing water from this circuit, the advantage of a secondary return is that hot water is always available near the point of use, preventing water from being wasted when e.g. a hot tap is used, and the cold water has to be run off before hot water is delivered.

Efficient insulation must be installed on the secondary circuit pipework so that heat loss from the circulating hot water is kept to a minimum.

Primatic hot water cylinder

A primatic or self-priming hot water cylinder is a vented indirect hot water cylinder which provides the water for the central heating circuit, preventing the need for a separate feed and expansion cistern. The two bodies of water – the central heating water and the domestic hot water inside the rest of the cylinder – are separated by one or more airlocks which are formed inside the heat exchanger as the cylinder is filled with water from the cold water storage cistern.

Although a plumbing system involving a primatic cylinder may be cheaper to install, it has significant long-term disadvantages:

  • Shower pumps should not be fitted to primatic cylinders due to the risk of disrupting the air bubble which separates the domestic supply and the central heating circuit.
  • Inhibitor chemicals and other additives cannot be added to the central heating circuit due to the risk of them contaminating the domestic hot water. The absence of a chemical inhibitor will increase the risk of corrosion and damage within the central heating system.

Fortic hot water cylinder

A fortic cylinder or combination cylinder is a vented cylinder with its own self-contained cold water storage cistern. These are ideal for flats, or households where it is impractical or not possible to install a separate cold cistern.

Fortic cylinders are available in both direct and indirect configuration, and are available in a range of capacities. It is also possible to buy primatic fortic cylinders.

Unvented hot water cylinder

As the name implies, unvented cylinders do not contain water at atmospheric pressure. This is because they are fed directly by the mains, eliminating the need for a cold water storage cistern. Unvented cylinders are usually made out of stainless steel instead of copper, and are available in both direct and indirect configurations.

Unvented cylinders are significantly less common than vented cylinders. This is because they were not permitted in the UK until 1986, although they are becoming more and more popular. The main advantages are:

  • Hot water at mains pressure – much better flow rates in comparison to a gravity-fed system
  • No need for a bulky storage cistern and its associated pipework

Due to the risk of danger in association with storing hot, pressurised water, unvented cylinders can only legally be installed by G3 certified engineers, and the cylinder must have a label clearly showing the installer’s name.

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Broken coil

broken coil refers to a fault in a hot water cylinder in which the coil inside the cylinder is perforated, allowing water from the central heating circuit inside the coil to mix with water in the hot water cylinder.

Overview

An indirect hot water cylinder contains a coil of pipework which is connected to the central heating circuit. Hot water from the boiler flows into the coil at the top, transferring its heat to the water in the cylinder, and then exits the coil at the bottom. These two aspects are referred to as the flow and return.

The hot water cylinder provides hot water to domestic services in the home, such as the bath, shower, and hot taps. It should therefore never come into contact with the murky brown water that is circulated through the radiators, and is typically loaded with anti-corrosion chemicals. A broken coil will allow this to happen.

Symptoms

The most common symptom of a broken coil is a cistern which is continuously filling and another cistern which is continuously overflowing, even though the ball valve is working properly. The cistern overflowing is usually the feed and expansion cistern. This is because the level of water in the feed and expansion cistern is typically much lower than the water level in the cold water storage cistern due to its size – the cold water storage cistern can obviously accommodate a much greater volume of water.

A broken coil means that the two separate water systems – the domestic water supply and the central heating – effectively become a single system, and the water level in the two cisterns tries to balance out. However, the overflow in the cistern with the lower water level prevents this from happening, resulting in a cistern which is constantly overflowing, even though the ball valve is in good working order. This is due to water entering the cistern via the outlet at the bottom.

While the feed and expansion cistern is usually the cistern which overflows, the cold water storage cistern will also overflow if the water level in the feed and expansion cistern is higher.

Another symptom of a broken coil will be yellow or rust-coloured water from the hot taps. This is due to water from the central heating circuit entering the hot water cylinder via the coil. The water may have a chemical smell as a result of chemicals added to the central heating circuit, such as inhibitor and/or biocides.

Repairing a broken coil

A broken coil is usually the result of corrosion, and unfortunately the only way to repair it is to replace the hot water cylinder.

 

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How to drain the cold water tank

Need to drain the cold water tank? It’s not a difficult task, and in most cases you shouldn’t need to go into the loft. Simply do the following:

  1. Turn off the mains stopcock, either on the rising main or outside the property.
  2. Turn on the hot taps.

And that’s it – when they stop running, the tank should be empty. Well, not quite in fact – there will still be a small amount of residual water below the outlet points. If you need the tank to be completely empty, then this water will have to be bailed out, or removed with a wet vac.

If you can’t find the stopcock, or for some reason it is inaccessible, you will need to go into the loft and close the isolation valve on the supply to the ballcock with a screwdriver. If there isn’t an isolation valve, you can lay a piece of wood across the tank and tie the ballcock up with a length of string or garden twine.

An empty tank is a splendid opportunity to remove any limescale or sediment which may have gathered in the bottom – or dead rodents and insects. Buy a lid to prevent any animals or loft debris from getting in the tank – you should be able to get one that suits its shape and capacity. Ideally, you should fit a Byelaw 30 kit (or Byelaw 60 kit if you live in Scotland). These kits consist of a number of components which protect the water from external contamination.

Draining the cold water tank will also stop the flow of hot water in your house, as it is gravity acting on the water in the loft which effectively pushes hot water out of the top of the hot water cylinder. Consequently, this means that draining the cold tank will not empty the hot water cylinder – the hot water in the cylinder will simply be replaced with cold water from the cold water tank until the tank is empty. If you want to drain the hot water cylinder, you will need to shut off the supply from the cold water tank and attach a hosepipe to the draincock on the supply pipe to the cylinder.

If you have an indirect plumbing system, i.e., your bathroom taps are supplied via the cold water tank, then you should open the cold taps in the bathroom until the tank is empty. This will save you from having to waste all of the hot water in the hot water cylinder.

Refilling the tank is easy: simply ensure that all taps and drain-off points are closed. Untie the ball valve, or open the isolation valve or stopcock. If you have carried out any maintenance on the cistern while it was empty, then you should check it for leaks while it is filling.

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Tank connector

tank connector or tank coupler is a fitting which connects a pipe to a cistern, allowing water to be drawn from the cistern, and in some circumstances, allowing water to enter it.

Tank connectors are typically found on cold water storage cisterns and feed and expansion cisterns. They are usually made out of brass and accommodate the pipe via a compression fitting, although plastic push-fit tank connectors can be purchased. Tank connectors are typically available as 15mm, 22mm, and 28mm fittings.

A tank connector typically consists of a flange at one end and a compression fitting on the other. A washer is usually supplied with the fitting and should be secured via the flange on the inside cistern wall. A second washer for the outer cistern wall is recommended. Ideally, the flange will have a hexagonal shape so that a pair of adjustable grips can easily be used to secure the fitting in place.

Cold water storage cistern

A cold water storage cistern will have at least two tank connectors: one for the overflow, and one for drawing off cold water to supply the hot water cylinder. The connector for the overflow is normally a 22mm fitting in accordance with Byelaw regulations, or 28mm under Scottish regulations.

The connector for the hot water cylinder supply is usually a 22mm fitting, although a 28mm fitting may be necessary for larger households. Where the cold water storage cistern supplies cold water outputs, it is vital that the outlet for the hot water cylinder is fitted higher than the cold outlet, so that if the water in the cistern is exhausted, the hot water will stop flowing before the cold does. This means that an individual taking a shower will not be scalded if the water in the cistern runs out: the water will run cold, not hot.

In order to prevent the ingestion of sediment or limescale into the plumbing system, tank connectors should be fitted at least 50 – 75mm above the base of the cistern. However, water regulations recommend that, where possible, outlets should be fitted to the bottom of the cistern in order to prevent sediment from gathering in the first place. Tank connectors should be fitted on the opposite side of a cistern to the inlet, ensuring the circulation of water through the cistern in order to prevent stagnation.

Feed and expansion cistern

A feed and expansion cistern will also have two tank connectors: one for the overflow, and one for connecting the cistern to a 15mm feed pipe which supplies central heating system with water and allows for the water, when heated, to flow back up into the cistern as it expands. For this reason, this pipe should never be fitted with an isolation valve.

The water level in a feed and expansion cistern is adjusted so that when the central heating system is cool, the water level is only slightly higher than the outlet. This is so that the water in the central heating system has the space to expand when heated. The cistern must be able to accommodate the expansion of the water by approximately 4% of its original volume, and the elevated water level must be at least 25 mm / 1 inch below the overflow.

How to fit a tank connector

Installing a tank connector on a cistern is a simple task.

  1. Using a marker pen or crayon, mark the location of the tank connector on the cistern wall.
  2. Drill the hole using a 29mm hole saw for a 22mm tank connector, or a 22mm hole saw for a 15mm tank connector.
  3. Remove any swarf created by the drill.
  4. Insert the tank connector into the cistern wall, making sure that the rubber washer is on the inside. Fitting a washer to the outside of the cistern wall is recommend, and will offer an extra layer of security.
  5. Tighten the fitting to create a watertight seal.
  6. Use your fingers to check the fitting for leaks while the cistern is filling. If there are any leaks, drain the cistern and tighten the fitting as necessary. Tightening joints with water in the cistern is poor practice and could lead to disaster if the cistern ruptures.

Tips

  • Tank connectors and the adjacent plumbing of a cistern are usually brass compression fittings. In the event that a blowtorch has to be used in the vicinity of a plastic cistern, take exceptional care to protect the cistern from heat, including the transfer of heat along the pipework to the cistern wall. The use of blowtorches in loft spaces is not advisable due to the fire hazard.
  • In the event that a tank connector must be fitted to a galvanised cistern, the tank connector must separate the cistern wall from any copper pipework. This is to prevent a corrosive electrolysing reaction from occurring.
  • Never use oil-based jointing compounds to make cistern connections. Not only are they likely to contaminate the water in the cistern, they may cause an unwelcome chemical reaction with the plastic of some cisterns.
  • Never make a hole in a plastic cistern by heating a piece of pipework with a blowtorch and pushing it through the cistern wall. This may weaken the surrounding area of the cistern wall and affect its structural integrity. It is also liable to void the manufacturer’s warranty of the cistern.
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Part 2 ball valve

A Part 2 ball valve or diaphragm ball valve is a ball valve made to British Standard specification 1212, Part 2. It consists of a plunger and a diaphragm washer which are both situated inside a brass housing. The plunger is partly visible and protrudes from the face of the valve. Water enters the cistern via small plastic spout on the top of the valve which directs the water down into the cistern. The float arm is secured to the valve via a brass split pin.

When the water level in the cistern rises, the float arm pushes the plunger into the valve. The plunger in turn pushes the diaphragm washer onto the valve seating, closing the valve.

Contents

Overview

Part 2 ball valves are intended for mains-fed cold water storage cisterns and feed and expansion cisterns, and are by far the preferred choice over Part 1 ball valves. This is because Part 2 ball valves offer a much greater air gap between the water exit point on the valve and the water level in the cistern if it reaches “critical level”, i.e. the same level as the pipe centre line. Part 2 ball valves also have a specifically designed mechanism for adjusting the water level in the cistern, whereas the only way to do so on a Part 1 ball valve is to bend the float arm.

Current water regulations no longer permit the use of a Part 1 ball valve on a cold water storage cistern. While a faulty Part 1 ball valve on a pre-existing installation can be repaired, it should ideally be replaced with a Part 2 ball valve – especially if the old valve has a rigid tube which dips down into the water in the cistern. These ‘silencer’ tubes are prohibited by water byelaws.

 Faults

A faulty ball valve is the most common cause of cistern overflow. The float can become perforated and sink, or the arm can become jammed down by limescale or debris. The arm can also become jammed up, preventing the cistern from refilling.

The most common reason for a Part 2 ball valve to fail is wear and tear on the washer and/or on the valve seating, which prevents the valve from shutting off.

Repair

Repairing a Part 2 ball valve is relatively straightforward, and can be achieved without undoing the tap connector attached to the valve stem and removing the entire assembly from the cistern. While holding the valve body with a pair of grips, use an adjustable spanner to loosen the nut against the cistern wall. Undo the nut while holding the valve body in place with your hand, and the valve can be removed. Take care not to drop the washer into the cistern as you remove the valve.

Once you have you removed the valve, you can disassemble it, and fit a new washer or valve seating as necessary. If you are replacing a Part 1 ball valve with a Part 2 ball valve, you can simply undo the valve nut on the new valve, and screw it into the pre-existing fitting on the cistern.

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Byelaw 30 and Byelaw 60 kits

Byelaw 30 kits and Byelaw 60 kits consist of a set of components designed to protect the water in a cistern from contamination. They are intended for mains-fed cold water storage cisterns and feed and expansion cisterns, and are either supplied with a new cistern, or can be purchased separately if one is looking to upgrade an existing installation. The variation in name is due to the separate legal systems in the UK, namely England and Wales, and Scotland. The main difference between the two kits is the diameter of the overflow: a larger diameter is stipulated by the Scottish Byelaw 60.

The kits generally consist of a screened overflow pipe, an overflow dip tube, a rubber grommet for the expansion/vent pipe, and a breather fitting. In compliment with the cistern lid, they play an instrumental part in keeping the water in the cistern free from dirt and debris. Depending on the manufacturer, some kits may include a Part 2 ball valve and/or a small ball valve backing plate.

Overview

Cisterns fed from the mains form an important part of any household plumbing system. Without any protection, they will ingest unwanted debris from the loft, risking the blocking and contamination of your plumbing systems.

Byelaw 30 and Byelaw 60 kits typically include the following items:

  • A rubber grommet, to create a sealed admission point for the expansion pipe/vent pipe.
  • A screened breather, fitted into the lid in order to prevent the formation of condensation inside the cistern and keep it at atmospheric pressure.
  • A screened overflow pipe, to prevent anything outside, such as insects, from entering the cistern.
  • A dip tube, allowing the overflow pipe to dip into the water so that cold drafts cannot enter the cistern.

The difference stipulated by the different codes is that the overflow dip tube must be 38mm (1.5 inch) in order to satisfy Byelaw 60 in Scotland, whereas 22mm (3/4 inch) is suitable for Byelaw 30 in England and Wales.

Water regulations also require that cisterns have a close-fitting lid which will not react with the water, and will retain its structural integrity should it get wet. The lid plays a vital role in keeping any animals from getting into the cistern, such as insects, rodents or even birds.

Some byelaw kits may include a small plastic backing plate, which is secured to the outer cistern wall via a nut on the stem of the ball valve. This reduces stress to the cistern wall from the upward force of the float. Some byelaw kits may include a ball valve – usually a Part 2 model.

 

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Feed and expansion tank

Need a new feed and expansion tank? Check prices at B&Q

The feed and expansion tank, or feed and expansion cistern as it is technically known, is a cistern which supplies the central heating circuit with water and accommodates the expansion of the water when it is heated by the boiler. It is often informally known as the header tank. It is typically made out of plastic, although like cold water storage cisterns, other materials have been used in the past, such as asbestos or galvanised steel.

The feed and expansion cistern is usually situated in the loft – often near the cold water storage cistern – and forms the highest point of the central heating system. It is supplied by the rising main, and is generally the smaller of the two cisterns: in a typical home, it will have a capacity of around 4 gallons (18 litres).

Contents

General overview

The flow of water into the cistern is controlled by a ball valve. Should the ball valve fail or water enter the cistern in the event of a broken hot water cylinder coil, an overflow pipe carries the water away, discharging outdoors. The overflow pipe should be fitted at a constant fall, and its exit outside should be clearly visible so as to alert the homeowner to a fault. The overflow should be at least 19mm in diameter, and should be capable of evacuating all of the excess water under maximum fault conditions, such as in the complete failure of the ball valve. An isolation valve must be fitted to the mains pipe supplying the cistern.

A tank connector connects the cistern to a feed pipe which supplies the central heating system with water and allows for the water, when heated, to flow back up into the cistern as it expands. This pipe should be at least 15mm in diameter and must never be fitted with an isolation valve.

Another pipe connected to the central heating system rises up above the cistern to form a ‘U’ shape, and points down into it without coming into contact with the water. This pipe is known as the vent pipe, and serves as an exit point for any air which may have got into the system or any gases which may have formed inside it, such as hydrogen. The vent pipe should be at least 22mm in diameter, and should rise at least 450mm above the maximum water level in the cistern in order to prevent the system from pumping over. This fault may also occur when the pump is installed incorrectly or is set at too high a speed, causing water to discharge into the cistern through the vent pipe. This process enriches the water with oxygen, much like an aerator in a fish tank, and the oxygen-rich water will quickly ruin the entire heating system via internal corrosion if left uncorrected. Similarly, the pump must not be installed in a position which will draw air into the system via the vent pipe.

Construction

Like the cold storage cistern, feed and expansion cisterns are generally made from plastics – either polyethylene, polypropylene, or polyvinyl chloride (PVC), although glass-reinforced polyester (GRP) may also be encountered.

Older cisterns may be made from galvanised steel, which is susceptible to corrosion. Some cisterns may also be made from asbestos cement, and just like cold water storage cisterns, you should never attempt to cut up or even dispose of asbestos cisterns yourself. Even in tiny amounts, asbestos particles are extremely dangerous to human health; skin contact alone can cause nasty dermatological problems. Contact a professional asbestos remover – it’s just not worth the risk.

Some cisterns may be made entirely from copper. Metal cisterns are required where water is heated by a device without any form of thermostatic control, because they may vent extremely hot water into the cistern even as part of their normal operation.

Modern plastic cisterns are generally black in order to resist algae growth, and are usually rectangular or loosely rectangular in shape. A lid is not always necessary, as some cisterns have an ‘enclosed’ style design with a built-in service hatch on the top.

Base and location

The feed and expansion cistern is obviously not as heavy as the cold water storage cistern. Nevertheless, it must conform to exactly the same regulations, and should be situated on a flat, stable, continuous base that extends at least 50mm beyond each side of the cistern and will retain its structural integrity if it comes into contact with water. Marine-grade plywood of at least 19mm is recommended. Chipboard should never be used as it is liable to disintegrate if it gets wet.

In most households, the feed and expansion cistern will be located near or next to the cold water storage cistern. On older installations, you may find that it is suspended directly above the cold water storage cistern via a base or joists across the larger cistern. In some cases, the overflow and/or the vent pipe may simply discharge into the cold water storage cistern, risking the contamination of the domestic water supply with the dirty water that circulates through the central heating system. Such installations are as inadequate as they are dangerous.

Contents

The ball valve in a feed and expansion cistern is adjusted so that when the central heating system is cool, the water level is only slightly higher than the outlet at the base of the cistern. This is so that the water in the central heating system has the space to expand when heated. The cistern must be able to accommodate the expansion of the water by approximately 4% of its original volume, and the elevated water level must be at least 25 mm / 1 inch below the overflow.

An inhibitor solution must be added to the central heating system in order to prevent internal corrosion and the formation of oxides. This is easily added via the cistern, and can be done once the heating system has been drained down and flushed out. Bacteria and mould spores can cause the formation of a foul smelling jelly or skin on the surface of the water; this can be prevented by adding a biocide to the cistern.

Loaded with anti-corrosion and biocide chemicals, the stale, recirculating water of the central heating system should obviously never come into contact with the domestic hot water . However, this will happen in the event that the coil in the hot water cylinder develops a leak, and of the two cisterns in the loft, will cause the one with the lower water level to overflow – usually the feed and expansion cistern, as its water level tries to balance out with the higher water level in the cold water storage cistern.

Extra fittings

The cistern and all its adjoining pipes must be lagged in order to prevent them from freezing during the winter. Loft insulation should not be placed underneath the cistern, as heat rising from the household below during the winter will help prevent this.

A small backing plate, either metal or plastic, and located on the outside cistern wall, is secured via the ballcock’s rear nut. This reduces stress to the cistern wall from the upward force of the float.

A close-fitting lid is required, and will prevent dust, insects and rodents from getting inside, as well as bits of loft insulation and other debris which could cause a blockage or damage in the central heating system.

Water byelaws require the fitting of certain components in order to minimise the risk of contamination. These are:

  • A rubber grommet, to create a sealed admission point for the vent pipe.
  • A screened breather, to keep the cistern at atmospheric pressure.
  • A screened warning pipe unit, to prevent anything outside, such as insects, from entering the cistern.

These parts can be bought as a kit. Byelaw 30 kits, as they are known, are often supplied with a new cistern, but they can also be purchased separately if you are looking to upgrade an older cistern. They will also include a dip tube which allows the warning pipe to dip into the water so that cold drafts cannot enter the cistern, although this is less likely to be of much use, as unlike a cold water storage cistern, the default water level in a feed and expansion cistern will usually be well below the overflow.

Where to buy

Brand new feed and expansion tanks for new installations or to replace an existing cistern are available from most of the major UK hardware stores. B&Q sell a 4 gallon cistern from Polytank, which comes complete with an insulation jacket, a Part 2 ball valve and float, a ball valve backplate, a 15mm compression tank connector, a warning pipe elbow, and a lid. You can also purchase a feed and expansion tank from Wickes, although none of the extra components are included, and the Polytank cistern from B&Q is likely to be a better choice. B&Q offers a click-and-collect service, and free delivery on orders over £50.

B&Q

Wickes

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Overflow pipe leaking: why is it leaking & how to fix it

Overflow pipe leaking? In this guide, we’ll tell you how to identify the problem and how it can be fixed.

A leaking overflow pipe means that water is entering a cistern when it shouldn’t. This is usually due to a faulty ball valve. The first thing to do is to identify which of the cisterns in your house is overflowing – if the overflow pipe is at ground floor or first floor level, then the toilet cistern is probably the culprit. If the leaking overflow pipe is at loft level or protrudes from the eaves of the roof, then the source is either the cold water storage cistern, or the smaller feed and expansion cistern, if you have one. In all cases, if you do not know which is the problem cistern, then a visual inspection will tell you. If it’s not immediately obvious, take a look at the water level. If it is extremely close to the overflow, or higher than the level marked by residual limescale, then that may indicate the cistern in question. Remember that it may take hours for a small leak to raise the water level in a cistern enough for it to overflow. Normal water use in the home during the day may disguise a dripping overflow until the early morning, when a faulty ball valve has dripped all night into the cistern.

Check the ball valve. If the water is running continuously, is the arm down? Move it up and down – this may release it if it has got stuck. If the arm won’t rise when you lift it and release it, then the float is likely to have become waterlogged and will need to be replaced.

If the arm moves freely and the float is watertight, but the valve still does not shut off properly, the washer and/or nozzle may be worn, and will need to be replaced.

If you are absolutely certain that the valve shuts off normally and at the desired level, then the problem can only be water entering the cistern through the outlet pipes at the bottom.

The cause of this fault relates to one of either two aspects of your plumbing system: a mixer tap or shower, or an indirect hot water cylinder.

Mains pressure water is at a much higher pressure than gravity-fed water, such as the hot water from your hot water cylinder. Where mains pressure water and low-pressure water mix, the mains pressure water may displace the hot, and push it back through the hot water cylinder and back into the cold water storage cistern.

Think back – did the cistern only start to overflow after the recent installation of a device with a mixer valve? Or does it overflow when you have a bath or a shower? If so, then it is very likely that a mixer tap or mixer shower is the cause of the problem. Of course, this problem can also be caused by a pre-existing mixer tap or mixer shower developing a leak inside.

Another reason for a cistern to overflow – and indeed the only possible reason, if the ball valve is in working order and you do not have any water mixing outlets – is that the coil in the hot water cylinder has a hole in, most probably due to corrosion. In the event of a broken coil, it is the smaller feed and expansion cistern which is most likely to overflow, due to the lower water level trying to balance out with the level in the cold water storage cistern. The only solution to this problem is to replace the hot water cylinder.

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Part 1 ball valve

A Part 1 ball valve or Portsmouth ball valve is a ball valve made to British Standard specification 1212, Part 1. It consists of a piston inside a brass housing, with a float arm secured to the valve via a split pin. Inside the piston is a slot which accommodates the end of the float arm, and on one end of the piston is a washer. When the water level in the cistern rises, the arm pushes the piston and its washer onto the valve seating, closing the valve.

Part 1 ball valves are gradually being phased out in favour of Part 2 and Part 3 ball valves. Unlike these valves, Part 1 ball valves do not offer an effective air gap in the event that the water level reaches the pipe centre line, due to the position of the water outlet at the lowest point of the valve housing. Also, they are not equipped with a mechanism to adjust the position of the float and thus the level of water in the cistern: the only way to do so is to bend the float arm. Some Part 1 ball valves on pre-existing installations may have a rigid plastic or metal tube which dips into the body of water in order to reduce the sound of running water as the cistern fills – these ‘silencer’ tubes are no longer permitted by water byelaws.

For these reasons, Part 1 ball valves are no longer permitted on cold water storage cisterns due to non-compliance with water byelaws. They may be found on older installations, and should ideally be replaced with a Part 2 ball valve.

Faults

A faulty ball valve is the most common cause of cistern overflow. The float can become perforated and sink, or the arm can become jammed down by limescale or debris. The arm can also become jammed up, preventing the cistern from refilling.

The most common reason for a Part 1 ball valve to fail is wear and tear on the washer and/or on the valve seating, which prevents the valve from shutting off.

Repair

Repairing a Part 1 ball valve is relatively straightforward, and can be achieved without undoing the tap connector attached to the valve stem and removing the entire assembly from the cistern. First, isolate the water supply. Then, while holding the valve body with a pair of grips, use an adjustable spanner to loosen the nut against the cistern wall. Undo the nut while holding the valve body in place with your hand, and the valve can then be removed. Take care to make sure that the washer doesn’t fall into the cistern as you remove the valve.

Once you have you removed the valve, you can disassemble it, and fit a new washer , piston, or valve seating as necessary. If you are replacing a Part 1 ball ball valve with a Part 2 ball valve, you can simply undo the valve nut on the new valve, and screw it into the pre-existing fitting on the cistern.

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Overflow

An overflow is an important part of a cistern, and serves two purposes in the event of a fault: to take away excess water in order to prevent structural damage to a property, and to indicate to the homeowner that there is a problem – in most cases, a faulty ball valve. An overflow pipe which exits a property on the ground floor or from the first floor is likely the overflow for a toilet cistern; an overflow pipe which exits at the level of the loft or protrudes from under the eaves of the roof is likely the overflow for a cold water storage cistern or a feed and expansion cistern.

There are two types of overflow generally found in household plumbing: side entry, and bottom entry. Bottom entry overflows tend to be found in toilet cisterns. The overflow in a cold water storage cistern is almost always side entry, and water regulations require that the overflow dips into the surface of the water in order to prevent cold drafts from entering the cistern, and that there is a filter screen to prevent insects from getting inside. These items are available as part of a Byelaw 30 kit. The water level in the cistern must be at least 25mm below the overflow when the cistern is full and the ball valve is closed. The overflow should be at least 19mm in diameter, and should be capable of evacuating all of the excess water under maximum fault conditions, such as in complete failure of the ball valve.

As previously stated, the most common cause of an overflowing cistern is a faulty ball valve. However, there are circumstances in which a cold water storage cistern or feed and expansion cistern can overflow, even with the ball valve in working order. A common reason for the feed and expansion cistern to overflow in this way is a perforation in the hot water cylinder’s coil. This effectively merges the domestic water system with the central heating circuit, and gravity tries to equalise the water level between the two cisterns. As the feed and expansion cistern is generally the cistern with the lower water level, the water level will rise in order to level off with the cold cistern, but the overflow prevents this from happening. The only way to resolve the issue is to replace the hot water cylinder.

A common reason for a cold water storage cistern with a working ball valve to overflow is a mixer valve, such as a shower or mixer tap, which is plumbed into the mains. When the tap or shower is open, the higher pressure mains water displaces the hot water and pushes it back the way it came, effectively filling up the cistern from its outlet.

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